Studies on the structure-function analysis of murine Ia molecules will be done utilizing Ia molecules altered by site-directed in vitro mutagenesis. Murine AK alpha or AK beta molecules will be altered by substituting the d allele specific residues at each of the polymorphic positions within the alpha-1 or beta-1 domains. Substitutions will be made one residue at a time or entire allelically variable regions will be changed such that the alpha- 1 or beta-I domains are more like the d allele sequence. The altered genes will be transfected into M12.C3 cells or L cells by electroporation and the cells tested for loss and gain alterations in k or d allele specific serologic epitopes or antigen presentation function to T cell hybrids. These mutants will also be utilized to identify regions on the Ia molecule that are important for alpha/beta chain pairing and for intracellular transport.